Insulin pumps are used to precisely control the amount of insulin injected in diabetic patients. Patients with more severe conditions may need multiple injections of insulin per day to maintain a reasonable blood sugar level. Insulin pumps can improve the quality of life of patients, and reduce the risk of complications due to long-term illness by rationally controlling blood sugar. The firmware design allows for adjustment of the drug dose and syringe injection rate, allowing the patient to adjust the amount of insulin injected according to (or estimated) feeding, sleep and exercise conditions.
The insulin is placed in a user-replaceable needle tube that is placed in the pump body to form a dedicated syringe with a piston that is slowly depressed under the control of the pump. The needle outlet is connected to a hose and insulin is injected through the hose into the patient's skin (usually in the abdomen).
The blood glucose meter continuously monitors diabetic patients and provides real-time blood glucose indicators through subcutaneous sensors. Each time the sensor is replaced, it can be used for several days without the patient having to repeatedly collect blood samples. The future development trend is to further improve the blood glucose detection, response mechanism and the synergy of the entire loop of the automatic adjustment of insulin dosage.
FDA regulation of medical equipment
The insulin pump is a portable medical device. In the United States, the design and production of insulin pumps are regulated by the US Food and Drug Administration (FDA). This means that their design and architecture must meet the requirements of the filing documents, performance must meet strict regulations and development testing, production testing, on-site maintenance requirements.
The device must also have self-test and fault indication capabilities, which require additional support circuitry and components to perform the self-test feature.
Considering the time and cost of obtaining FDA approval, insulin pump manufacturers need to choose a customer-oriented chip supplier that can strictly control the shutdown policy to ensure that system vendors are maintained for several years.
The reason that medical device manufacturers trust Maxim is that we have always been cautious about the discontinuation of the device. We clearly understand the serious damage caused by the discontinuation of the device to medical device manufacturers, and constantly relocate some old products to the new product line. Establish wafer inventory, provide last-time procurement opportunities or develop new upgrade replacement products. Maxim rarely discontinues a device when the customer still needs it. Maxim's device shutdown policy is also the most flexible compared to competitors.
Portability
Insulin pumps are portable devices that must be small, lightweight, and so on. A typical insulin pump measures approximately 2 in x 3 in x 0.75 in. and weighs only 2 to 4 ounces. This small form factor requires designers to prioritize size and power consumption when selecting components.
To save space, system designers need highly integrated, ultra-small packaged devices such as UCSPTM packages and wafer level packages (WLPs). In order to use batteries as small as possible, designers must do everything possible to reduce power consumption and increase efficiency. If possible, put any unused circuitry in shutdown mode.
Insulin pump solution
How the insulin pump works
Insulin is measured in "units" and is divided into 100 units per cc (or mL), assuming a standard concentration of U-100. In this metering mode, one unit is equivalent to 10 μL. The injection rate is 1 unit/hour, and each injection is 3 to 10 minutes. The dose of one piece of insulin is several units. Typically, the needle can be filled with 200 to 300 units of insulin.
Taking into account the extremely low flow rate, the motor drives the operation of the gear-driven pump step by step, driving the piston of the needle tube to move very slowly. Usually only the angle of the motor needs to be roughly measured. Most insulin pump manufacturers use optical encoders and DC motors, as well as stepper motors. In order to reduce the size of the system, you can also choose to use MEMS pump or pressure pump, thus eliminating motor control.
Flow detection
Use a pressure sensor to detect the seal of the system and ensure proper operation. Based on silicon strain gauges, the output signal amplitude of these sensors is on the order of millivolts, while the output signal range of the bond line strain gauge is on the order of microvolts. The stress meter uses a typical bridge structure to generate a differential signal based on the common-mode voltage. The common-mode voltage is typically half the supply voltage.
The design can use an analog-to-digital converter (ADC) with a differential input programmable gain amplifier (PGA), or a microcontroller with an internal ADC and an external differential amplifier or instrumentation amplifier (for signal conditioning). Pressure measurements do not require high precision because pressure readings are only used to indicate that work is normal and are not used for injectable dosing.
Power supply
Insulin pumps typically use a step-up regulator that boosts the low-voltage (1.5V, nominal) input of a single alkaline battery to 2V or higher. To take full advantage of battery energy, the boost converter should be able to operate at the lowest possible input voltage. Maxim's boost converters are capable of operating at voltages as low as 0.6V and start-up voltages as low as 0.7V, making efficient use of battery power.
If the device requires a strictly stable supply voltage, the boosted power supply may need to be further regulated in the design. In such low voltage applications, linear regulators provide higher efficiency due to the absence of switching losses (intrinsic losses in switching power supplies). Although the buck regulator with skip mode has higher efficiency at light loads, a low dropout linear regulator (LDO) can achieve a smaller solution size, which is especially important for insulin pumps. The efficiency of LDO is very close to the ratio of VOUT/VIN. Higher efficiency can be obtained when the difference between VIN and output voltage is slightly higher than the LDO differential.
If the motor requires a regulated source to supply power, a switch mode converter can be selected. To reduce the size and weight, you can choose the converter with the highest switching frequency. For multi-supply systems, a Power Management IC (PMIC) can be selected.
Battery management
Insulin pump manufacturers have made great strides in reducing power consumption and extending battery life. The insulin pump currently used on the market can work for 3 to 10 weeks for each battery replacement or charge, and most insulin pumps use AA or AAA alkaline batteries or lithium batteries. The use of primary batteries (non-rechargeable batteries) is very popular, but the use of rechargeable batteries helps to save long-term costs. Since the capacity of the rechargeable battery is relatively low, the number of times of charging is relatively frequent.
Due to size constraints, most insulin pumps use primary batteries to save the charger. Due to the lack of a corresponding fuel gauge, the battery gauge mainly uses simple voltage measurement, and sometimes combined with temperature measurement. The system sends the voltage and temperature signals to the ADC for quantization. The microcontroller processes the data and uses a lookup table to determine the remaining battery capacity. Then the battery value is sent to the display (usually a battery icon, divided into several squares on the icon to show the remaining battery power), when the battery drops to the last cell, the insulin pump generates a low battery voltage alarm.
Programming characteristics
As mentioned above, the patient needs to adjust the dose of the drug according to the specific needs. This adjustment is achieved by a relatively simple interface, for example, the user only needs to control a few buttons. Users can also set up several tips to help manage the insulin dose.
Display/keyboard
Most insulin pumps use a monochrome, custom-character liquid crystal display (LCD), and a few insulin pumps use a color display. The display provides information on insulin injection dose, injection speed, battery remaining capacity, time, date, reminder information, and system alarm conditions (eg, atresia or insulin reserve is too low). The FDA requires the monitor to perform a self-test at power-on and requires a built-in self-test feature in the design. In addition, it is often necessary to provide the user with an audiovisual response to the touch screen input.
The new insulin pump includes continuous monitoring display. These systems use a continuous monitor with a wireless transmitter that transmits data through a wireless transmitter and reports the blood glucose levels detected by the sensor to activate pump injection when appropriate. The insulin pump also provides an analysis graph based on historical measurement data to guide the calculation of insulin injection volume.
Self-test function
According to FDA regulations, all insulin pumps must first run a self-test (POST) program to detect critical processor, circuit, indicator, display, and alarm functions. Some POST operations require user observation, and additional self-test circuits help reduce the potential for failure.
For example, some modules use a secure processor to monitor the operation of the main processor and will immediately signal an alarm if an unexpected condition is detected; some self-test systems may simply monitor the current through the on and off indications of the light-emitting diodes (LEDs). Once the current drops below the set threshold, a fault indication can be generated. The more common self-test circuit uses the watchdog timer (WDT), and the microprocessor monitoring circuit with WDT function monitors the running status of the program. Medical devices typically do not allow the integration of monitoring circuitry within the microprocessor IC itself, as the supervisory circuitry in this architecture may fail simultaneously with the processor.
The monitoring circuit is the key to ensuring that the insulin pump works properly during patient use. The microcontroller must be in a reset state before all supplies reach the tolerance range and remain stable. The voltage monitoring circuit monitors the overvoltage and undervoltage conditions of the power supply. It also needs to detect the running and shutdown conditions of the motor (motor failure is a serious system failure and the highest priority is given for alarms). The ADC can be built into the microprocessor or an external microprocessor to quantify the readings of the sensor (temperature, motor loading, insulin pump pressure, and battery voltage).
Alarm function
The insulin pump requires an audiovisual alarm to alert the user when a fault is detected, a specified time is reached, or certain warning conditions are triggered. LEDs can be used as visual indicators for remote blood glucose monitoring and insulin pumps. Green LED flashing usually means normal operation, and red LED signals are used to indicate alarm or warning status.
The buzzer must be equipped with a self-test circuit. The self-test circuit can indirectly monitor whether the impedance of the speaker is in the normal range. A microphone can also be installed near the speaker to directly generate an audio output to detect whether the level is in the normal range. Various operational amplifiers, comparators, audio amplifiers, microphone amplifiers, and other components are commonly used in the design of alarm and self-test functions. An audio digital-to-analog converter (DAC) can generate a unique alarm output signal.
An eccentric rotating block (ERM) motor is also used in the new insulin pump to generate a vibration alarm. ERM motor drives are not critical, but require an amplifier or regulator. A short ERM self-test is generated when the battery is installed.
Timing function
Given the stringent requirements for insulin injection safety, the system needs to record events and time-stamp changes to recorded data and processes. This feature requires a real-time clock (RTC) support, of course, the clock can also provide an alarm function.
Electrostatic discharge
All insulin pumps must meet the IEC 61000-4-2 Electrostatic Discharge (ESD) protection requirements, either with built-in protection or externally added ESD line protection devices. Maxim offers a variety of interface devices with higher ESD protection and an ESD protection diode array.
interface
Most insulin pumps provide a data port that can be used to send data to a computer or download upgrade firmware. With this feature, historical data can be imported into an application and sent to a monitoring center for support in the treatment of diabetes. The USB port is the most common data interface. The data port of the memory card should have ESD protection, current limit, logic level conversion and other functions.
RF interface
As mentioned above, some insulin pumps use an RF receiver to acquire data from a glucose continuous monitor. Most insulin pumps use Bluetooth® or an ISM band receiver.
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